The broad objective of this proposal is to develop synthetic methodologies towards next generation dental restorative composites that have a nanostructured arrangement of the inorganic and organic components, similar to the structures found in dentin and enamel. The self-hardening composites synthesized as part of this proposed work will have applications in the repair of dental cavities caused by caries. Our approach is to combine calcium phosphate minerals with the well-established ability of amphiphilic (hydrophobic/hydrophilic) block copolymers to direct the assembly of inorganic materials into mesostructured hybrids (with e.g., cylindrical, lamellar, or bicontinuous morphologies). We will start from amorphous calcium phosphate particles as a precursor phase, which, after structure formation with the block copolymers, will be crystallized to form robust composites with apatite (Ca10(PO4,CO3)6(OH)2) nanocrystals as the inorganic component. The synthesis of the materials will be completed with four specific aims: 1) Synthesis and characterization of stable amorphous calcium phosphate (ACP) particles (<100 nm) capable of forming stable suspensions in both aqueous and organic solvents. 2) Use of amphiphilic diblock copolymers to direct the assembly of ACP particles into materials with defined 1-D, 2-D, and 3-D nanostructures. 3) Controlled crystallization of the amorphous, inorganic phase of the nanostructured composites. 4) Development of self-hardening composites by mixing powders of the nanostructured composites developed in Aims 2 and 3 with an aqueous liquid phase to induce secondary crystallization. The design of these new composites for dental restoration represents a paradigm shift away from traditional materials with isolated inorganic particles embedded within a continuous polymer matrix to composites with a continuous inorganic phase penetrated by polymer. The benefits of a continuous inorganic phase include a reduction (or even elimination) of shrinkage of the composites as they harden, improved abrasion (wear) resistance, and stronger materials. Mechanically, the amphiphilic blockcopolymer as the organic component will provide toughness and fracture resistance to the composite. The adhesion of these self-hardening composites to the natural tooth should be better than the traditional resins since we are using a water-based system that will be able to infiltrate the hydrated dentin. The flexibility of the block copolymer system will allow us in the future to tailor the mesostructure of the composites to form materials whose mechanical properties best match the part of the tooth (e.g., dentin or enamel) being repaired. This research is consistent with the R21 philosophy in that the ability of amphiphilic block copolymers to phase segregate into nanostructured films has never been applied to the structuring of calcium phosphate mineralization.